1. Field of the Invention
The present invention relates to a nondestructive inspection device and a crane equipped with this nondestructive inspection device.
2. Description of Related Art
Recently, there has been an increase in the illegal importation of suspicious items hidden inside containers. Therefore, when importing and exporting containers, especially at a container terminal of a harbor, it has become increasingly important to quickly discover and uncover the suspicious items by inspecting inside the container. Particularly from the viewpoint of decreasing inspection manpower or maintaining the status of cargoes, there has been a demand for a method which allows nondestructive inspection from outside without opening the container.
As an inspection device that nondestructively inspects for suspicious items in a container, there is for example a straddle inspection system described in Published Japanese translation No. 2000-514183 of PCT (FIG. 1, FIG. 4). This straddle inspection system has a transmission radiation source and a detector which detects radiation, installed on a straddle crane having just sufficient space to enable a container to pass in between, and by self-propelling this straddle crane to relatively move the container between the transmission radiation source and the detector, a radiographic image of the container is obtained, and the presence of suspicious items is inspected for based on this radiographic image.
Here, according to the principle of detection, the detector can detect radiation intensity, but is unable to detect the incident direction of the radiation. That is to say, in the case where radiation is irradiated to the detector from a plurality of transmission radiation sources, the detector is unable to identify which transmission radiation source the radiation has been emitted from.
Therefore, conventionally, a radiographic image is obtained by irradiating radiation to one detector only from one transmission radiation source, in order to obtain an accurate radiographic image. Moreover in the case of performing inspection over a wide range where one transmission radiation source is unable to entirely irradiate transmission radiation, or in the case where radiographic images from a plurality of directions are required, a plurality of pairs of a detector and a transmission radiation source is provided. However, since detectors are extremely expensive, the inspection device becomes extremely expensive when a plurality of detectors is provided.
Moreover, the transmission radiation source is substantially a dot shaped radiation source, and the transmission radiation generated by the transmission radiation source gradually spreads as it becomes distanced from the transmission radiation source. That is to say, since the radiographic image of the container is larger than the container, the detector becomes larger than the container.
Since in this manner a large detector is used, the conventional inspection device is extremely expensive. Furthermore, when the detector becomes larger, the detector itself deforms due to its own weight, and it becomes difficult to obtain a high precision radiographic image.